1. Field of the Invention
The present invention relates to a plugged honeycomb structure, and more particularly, it relates to a plugged honeycomb structure capable of enhancing an isostatic strength and suppressing an increase in pressure loss and a decrease in capacity of deposited ash.
2. Description of Related Art
In exhaust gases discharged from an internal combustion engine such as a diesel engine, various burning devices, and the like, a large amount of particulate matter mainly composed of soot is included. Hereinafter, the particulate matter will be abbreviated to the “PM”. When the PM in the exhaust gas is discharged to the atmosphere as it is, an environmental pollution is caused. Therefore, in an exhaust system of the exhaust gas, a diesel particulate filter for collection of the PM is disposed. Hereinafter, the diesel particulate filter will be abbreviated to the “DPF”.
As the DPF, there has been used, for example, a honeycomb structure body having porous partition walls with which a plurality of cells are formed to define through channels of the exhaust gas and a purified gas. In this honeycomb structure body, plugged portions to plug open frontal areas of the cells are arranged in the open frontal areas of the predetermined cells at an end surface on an outflow side of the purified gas, and the open frontal areas of the remaining cells at an end surface on an inflow side of the exhaust gas, so that the honeycomb structure body is utilized as a plugged honeycomb structure (a honeycomb filter).
In the above plugged honeycomb structure, when the exhaust gas is allowed to flow into the inflow cells, particulates in the exhaust gas are collected by the partition walls during passage of the exhaust gas through the partition walls, and the purified gas from which the particulates have been removed is discharged from the outflow cells.
Heretofore, in the DPF, various catalysts have been loaded onto the partition walls of the plugged honeycomb structure, to perform purification of harmful components and the like in the exhaust gas. Moreover, as a honeycomb structure body for the purpose of uniformly loading the catalyst onto the partition walls, a honeycomb structure body having a hexagonal sectional shape in a cell extending direction has been suggested (e.g., see Patent Documents 1 to 3). Hereinafter, “cells having a hexagonal sectional shape in the cell extending direction” will be referred to as “the hexagonal cells”. Furthermore, a honeycomb structure body having porous partition walls with which the hexagonal cells are formed will be referred to as “the honeycomb structure body of the hexagonal cells”.
Additionally, a plugged honeycomb structure using the honeycomb structure body of the hexagonal cells will be referred to as “the plugged honeycomb structure of the hexagonal cells”.
Heretore, technologies have been suggested to prevent damages being caused to intersections of partition walls of a honeycomb structure body due to an excessively large heat shock or mechanical shock. For example, there has been suggested a ceramic honeycomb structure body in which one of facing corner portions is provided with a round portion having a substantially circular shape, in at least part of through channels (cells) in a cross section which is orthogonal to an axial direction (see, e.g., Patent Document 4).    [Patent Document 1] JP-B-H03-49608    [Patent Document 2] JP-T-2009-537741    [Patent Document 3] JP-A-2001-334114    [Patent Document 4] JP-A-2003-269131